Dear Wong, Jeremy,
Good question. HETERO supports FPGA but not VPU while MULTI does not support FPGA but supports HDDL, so that is one distinguishing difference between the two. Multi-Device plugin automatically assigns inference requests to available computational devices to execute the requests in parallel.Heterogeneous plugin is more about assigning affinity (specific layers) to a preferred device with a fallback policy. HETERO's main job is to utilize accelerators power and calculate heaviest parts of network on accelerator and execute unsupported layers on fallback devices like CPU.
Hope it helps,
I would look at the information of the pages
Honestly it depends on what you are trying to accomplish and how.